EN IEC 61400-6:2020/prA1:2024

SLOVENSKI STANDARD
01-junij-2024
Sistemi za proizvodnjo energije na veter - 6. del: Stolp in obravnava temeljnih
zahtev - Dopolnilo A1
Amendment 1 - Wind energy generation systems - Part 6: Tower and foundation design
requirements
Windenergieanlagen - Teil 6: Auslegungsanforderungen an Türme und Fundamente
Systèmes de génération d'énergie éolienne - Partie 6: Exigences en matière de
conception du mât et de la fondation
Ta slovenski standard je istoveten z: EN IEC 61400-6:2020/prA1:2024
ICS:
27.180 Vetrne elektrarne Wind turbine energy systems
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

88/1007/CDV
COMMITTEE DRAFT FOR VOTE (CDV)
PROJECT NUMBER:
IEC 61400-6/AMD1 ED1
DATE OF CIRCULATION: CLOSING DATE FOR VOTING:
2024-04-05 2024-06-28
SUPERSEDES DOCUMENTS:
88/937/RR
IEC TC 88 : WIND ENERGY GENERATION SYSTEMS
SECRETARIAT: SECRETARY:
Denmark Mrs Christine Weibøl Bertelsen
OF INTEREST TO THE FOLLOWING COMMITTEES: PROPOSED HORIZONTAL STANDARD:

Other TC/SCs are requested to indicate their interest, if any, in this
CDV to the secretary.
FUNCTIONS CONCERNED:
EMC ENVIRONMENT QUALITY ASSURANCE SAFETY
SUBMITTED FOR CENELEC PARALLEL VOTING NOT SUBMITTED FOR CENELEC PARALLEL VOTING
Attention IEC-CENELEC parallel voting
The attention of IEC National Committees, members of CENELEC,
is drawn to the fact that this Committee Draft for Vote (CDV) is
submitted for parallel voting.
The CENELEC members are invited to vote through the CENELEC
online voting system.
This document is still under study and subject to change. It should not be used for reference purposes.
Recipients of this document are invited to submit, with their comments, notification of any relevant patent rights of which they are aware
and to provide supporting documentation.
Recipients of this document are invited to submit, with their comments, notification of any relevant “In Some Countries” clauses to be
included should this proposal proceed. Recipients are reminded that the CDV stage is the final stage for submitting ISC clauses. (See
AC/22/2007 or NEW GUIDANCE DOC).

TITLE:
Amendment 1 – Wind energy generation systems – Part 6: Tower and foundation design requirements

PROPOSED STABILITY DATE: 2027
NOTE FROM TC/SC OFFICERS:
In 88/926/RQ, Result of 88/914/Q: Proposed amendment to IEC 61400-6:2020, Wind energy generation systems - Part 6:
Tower and foundation design requirements, it was concluded that MT 6 will have to further decide on the next step during
the preparatory stage of the amendment.
MT 6 has during to the development of the amendment, decided to submit the document directly as CDV.

electronic file, to make a copy and to print out the content for the sole purpose of preparing National Committee positions.
You may not copy or "mirror" the file or printed version of the document, or any part of it, for any other purpose without
permission in writing from IEC.

88/1007/CDV – 2 – IEC 61400-6:2020/AMD1  IEC 2024
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
WIND ENERGY GENERATION SYSTEMS –

Part 6: Tower and foundation design requirements

AMENDMENT 1
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their prepa-
ration is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may
participate in this preparatory work. International, governmental and non-governmental organizations liaising with
the IEC also participate in this preparation. IEC collaborates closely with the International Organization for Stand-
ardization (ISO) in accordance with conditions determined by agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all inter-
ested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any misinter-
pretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications trans-
parently to the maximum extent possible in their national and regional publications. Any divergence between any
IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and ex-
penses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
Amendment 1 to IEC 61400-6:2020 has been prepared by subcommittee MT 6: Tower and foun-
dation design, of IEC technical committee TC88: Wind energy generation systems.
The text of this Amendment is based on the following documents:
Draft Report on voting
88/xxxx/FDIS 88/xxxx/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Amendment is English.

IEC 61400-6:2020/AMD1  IEC 2024 – 3 – 88/1007/CDV
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are de-
scribed in greater detail at www.iec.ch/publications/.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
88/1007/CDV – 4 – IEC 61400-6:2020/AMD1  IEC 2024
1 INTRODUCTION
2 Sections as given in this document are replacing or amending the respective sections of IEC
3 61400-6:2020. The main part of this amendment concerns updated knowledge for the design of
4 L-flanges and modifications required due to changes to IEC 61400-1.
6 The previous method of fatigue assessment using the Schmidt/Neuper trilinear bolt force curve
7 approximation has been removed from the standard. It has been replaced with a physically
8 more accurate method.
10 The updated methodology for fatigue assessment of L-flanges has been calibrated such that
11 the target failure probability defined in IEC 61400-1 is achieved. Where existing flange designs
12 are checked with the updated method, over-utilization may be found, which in some cases may
13 show an order of magnitude higher than nominally acceptable damage.
15 This does not impose an immediate risk for the turbines affected, though, due to the following
16 factors:
18 a) In most cases such designs have significant conservatism in the fatigue loads assumed
19 e.g. due to the assumption of uni-directional wind combined with type class turbulence
20 conditions.
21 b) Experience shows that broken bolts are almost always found and replaced before a
22 turbine collapses.
24 Existing flange designs need not be re-assessed using the new method, and existing type or
25 project certification remains valid. In cases where broken bolts are found in operating turbines,
26 the affected flange should be checked with the new methodology. Based on the assessment
27 results and the root causes analysis for the failure, further measures should be defined (e.g.
28 shorter inspection intervals).
29 2 Normative references
30 Add the following normative references to IEC 61400-6:2020.
31 The following documents are referred to in the text in such a way that some or all of their content
32 constitutes requirements of this document. For dated references, only the edition cited applies.
33 For undated references, the latest edition of the referenced document (including any amend-
34 ments) applies.
35 ISO 898-1, Mechanical properties of fasteners made of carbon steel and alloy steel – Part 1:
36 Bolts, screws and studs with specified property classes – Coarse thread and fine pitch thread
37 ISO 898-2, Fasteners – Mechanical properties of fasteners made of carbon steel and alloy steel
38 – Part 2: Nuts with specified property classes
39 ISO 898-3, Mechanical properties of fasteners made of carbon steel and alloy steel - Part 3:
40 Flat washers with specified property classes
41 ISO 16047, Fasteners - Torque/clamp force testing
42 ISO 4759-1, Tolerances for fasteners – Part 1: Bolts, screws, studs and nuts – Product grades
43 A, B and C
44 ISO 4759-3, Tolerances for fasteners - Part 3: Washers for bolts, screws and nuts - Product
45 grades A, C and F
46 ISO 965 (all parts), ISO general purpose metric screw threads
IEC 61400-6:2020/AMD1  IEC 2024 – 5 – 88/1007/CDV
48 3 Terms and definitions
49 Add the following definitions to IEC 61400-6:2020.
50 3.1
51 Bolt assembly
52 Bolt assemblies comprise fastener, nut(s), optionally washer(s), preloading method and lubri-
53 cation system
54 EXAMPLE A stud assembly for tension-tightening may comprise a stud and two roundnuts on each side, without
55 additional washers
56 NOTE In this standard, the term “bolts” is used for the fastener elements. Instead of (head) bolts, also partially or
57 fully threaded studs with nuts on both ends may be used, if they have the same nominal thread geometry and material
58 properties as bolts from accepted standards.
59 3.2
60 Design gap height
61 k
design
62 Design gap height, defined as the 95% fractile value of the log-normal distribution defined by
63 k and COV (section 6.7.5.2)
mean k
64 3.3
65 Unloaded gap height limit
66 k
limit,unloaded
67 Allowable maximum gap height after mating of flanges, without influence of loading by dead
68 weight of tower section(s) above the flange or preload of bolts
69 3.4
70 Loaded gap height limit
71 k
limit,loaded
72 Allowable maximum gap height after mating of flanges, and after application of e.g. dead weight
73 of tower section(s) above the flange and/or partial preload of bolts
74 NOTE Conditions at time of measuring the loaded gap height shall be defined by the designer
75 3.5
76 Flatness deviation of individual flange
77 u
tol
78 Allowable flatness deviation as defined in section 6.7.3.1 for the individual flange
80 4 Symbols and abbreviated terms
81 Symbols
82 a flange dimension (nominal distance from inside of flange to bolt circle diame-
83 ter)
84 A nominal area of the bolt shaft with diameter d
85 a* auxiliary value to compute bolt bending moment
86 a’ reduced effective flange dimension according to Tobinaga/Ishihara
87 A flange cross section area in circumferential direction
cf
88 A nominal stress area of the bolt in thread
S
89 b weld neck thickness (normally equal to the thickness of the connected tower
90 shell) (in section 6.3.2.3 only)

88/1007/CDV – 6 – IEC 61400-6:2020/AMD1  IEC 2024
91 b flange dimension (nominal distance from bolt circle diameter to middle sur-
92 face of connected tower shell)
93 b’ distance in between plastic hinges for failures modes B, D, E
{B,D,E}
94 c flank height of the weld preparation (in section 6.3.2.3 only)
95 c segment width measured at the middle surface of the shell (tower wall)
96 c segment width measured at the bolt circle diameter
bcd
97 C stiffness of the compression spring q (representing the compressed parts)
D
98 COV coefficient of variation
99 COV coefficient of variation of gap height
k
100 COV coefficient of variation of preload force
p
101 C spring stiffness of the tension spring (representing the bolts)
S
102 d nominal diameter of the bolt
103 D outer diameter of the flange connection
104 D auxiliary values to determine coefficients for bolt force polynomial
{1,2}
105 d diameter of the bolt hole
b
106 DFT dry film thickness (DFT) of coatings applied to the flange surface beneath
sbw
107 washers (sbw), i.e in the contact area between washers and flange
108 D outside diameter of the washer
w
109 E Young’s modulus of steel
110 F * preload bolt force used for modified torque method
p,C
111 F ’ preload bolt force used in the design calculations (design preload)
p,C
112 F mean preload force after installation
p,inst.,mean
...